Axial flow compressor blades



AXIAL FLOW COMPRESSOR BLADES Original Filed Dec. l, 1966 E v E INVENTOR/2 Z/ I lfffex/f/ United States Patent O 3,403,893 AXIAL FLOW COMPRESSORBLADES Lewis J. Stofr'er, Cincinnati, Ohio, assignor to General ElectricCompany, a corporation of New York Continuation of application Ser. No.598,428, Dec. 1, 1966. This application Dec. 5, 1967, Ser. No. 695,818 4Claims. (Cl. 253-77) ABSTRACT OF THE DISCLOSURE A compressor blade isshown having incremental, inclined airfoil-shaped portions along itsleading edge, which portions are interconnected by other portions of theblade. The inclined and interconnecting portions are disposed on angleswithin specified limits. The teeth so formed are effective in reducingblade erosion, While maintaining desired aerodynamic characteristics.

The present application is a continuation of copending application Ser.No. 598,428, filed Dec. 1, 1966, now abandoned.

The present invention relates to improvements in gas turbine engineshaving axial flow compressors and more particularly to improved bladesfor such compressors.

One approach to increasing the performance of gas t-urbine engines, usedfor the propulsion of aircraft, has been to increase the diameter and/or the rate of rotation of the rotor of such compressors. The result hasbeen that the tangential velocity of the blade tips becomes extremelyhigh and often supersonic. Under these conditions of high tip speed,serious problems are encountered as a result of erosion caused by rainentrained in the air entering the compressor. Rain erosion, as well aserosion from dust particles, can seriously reduce the efliciency andoperating life of compressor blades even though normally the duration ofaircraft operation, under conditions where rain ingestion could occur,is relatively short under such conditions.

Compressor baldes are ordinarily made of high strength metal. Mucheffort in recent years has been expended in perfecting compressors whichare fabricated from various laminates, particularly those employingplastic resins reinforced with glass fibers. Such laminatedconstructions provide great savings in weight but are even more vulnerable to erosion from rain or dust particles entrained in the airentering and passing through such a compressor.

A somewhat similar erosion problem exists in steam turbines, and in U.S.Patent 1,862,827, it is taught that slots should be provided in theconvex surface of a turbine bucket and extend through the leading edgethereof to minimize the erosion effect of condensate particles in avacuum turbine. This teaching, however, is not applicable to compressorblades and particularly for compressors employed in gas turbine engineswhere a high degree of efficiency is required in order to obtainnecessary Weight and fuel consumption requirements.

Accordingly, it is an object of the invention to provide significantreductions in the erosive effect of rain or other particles entrained inan air entering and passing through a compressor and at the same timemaintain a high level of efiiciency in the operation of the compressor.

These ends are attained in a gas turbine engine having an axial flowcompressor which includes a bladed rotor "ice driven to compressor air,which may be used to support combustion or provide a propulsive force.The blades of the rotor are arranged in at least one circumferentialrow. It is also usual practice to provide a circumferential row of fixedblades immediately downstream of the rotating row of blades.

Each blade has an aerodynamic airfoil portion extending radially of theaxis of rotation of the rotor with leading and trailing edges relativeto the flow of air therepast. The leading edge portion of each blade hasa theoretical optimum curvature through approximately and usuallyslightly less than to opposite sides of the blade `which are equidistantfrom chord extending between the leading and trailing edges of theblade. In accordance with this invention, the leading edges of at leastthe first row of rotor blades, and optionally the stator blades, havesmall, lengthwise, incremental portions inclined at an angle between 30and 75 Irelative to the gas flow path approaching the blade. Theseinclined por-tions are interconnected by portions which are disposed onan angle of 030 relative to the gas ow path and are inclined in the samedirection relative thereto as the incremental inclined portions. Theinclined leading edge portions and ythe interconnecting portions formteeth having crotches protected by their tips from rain or the likeentrained in the airstream. By inclining incremental portions of theleading edge in the fashion described, a high resistance to erosion isobtained with little or no adverse effect on the aerodynamiccharacteristics of the blade, thus providing an efliciency in operationwhich approaches, if not equals, that of the conventional, theoreticaldesign.

It is further preferred that the inclined, incremental edge portionshave a cross section (relative to -the length wise direction of theblade) approximating that of said theoretical curvature. It is furtherpreferred thatthe interconnecting portions are substantially flat at thetips of the teeth and are progressively crowned toward the crotches sothat the crotches may lbe formed on a curvature which blends with thecurvature of the inclined p-ortions. 4

The above and other related objects and features of the invention willbe apparent from a reading of the following description of thedisclosure found in the accompanying drawing and the novelty thereofpointed out in the appended claims.

In the drawing:

FIGURE 1 is a diagrammatic view of a gas turbine engine;

FIGURE 2 is a compressor blade which would be used in such an engine;

FIGURE 3 is an enlarged fragmentary perspective view of the upperleading edge portion of this blade;

FIGURE 4 is an elevation of the leading edge portion of the blade,looking lat the concave surface of the blade;

FIGURE 5 is a View taken on line V-V in FIGURE 4;

FIGURE 6 is a section taken on line VI--VI in FIGURE 4;

FIGURE 7 is a line taken on line VIl-VII in FIGURE 4;

FIGURE 8 is a section taken on line VIII-VIII in FIGURE 4;

FIGURE 9 is a fragmentary perspective view of the upper leading edgeportion of a modified blade; and

FIGURE 1 illustrates the gas turbine engine environment of the presentinvention. The engine illustrated is of the turbofan type, comprising acore engine and a fan or low compressor 12. The core engine includes ahigh pressure compressor 14, a combustor 16, and a turbine 18. Air ispressurized by the compressor 14 to support combustion of fuel in thecombustor 16 to thereby generate a hot gas stream which passes throughthe turbine 18. The rotor of the compressor 14 is connected to theturbine 1=8 and driven thereby. The hot gas stream then passes through asecond compressor 20 which is connected to the rotor 26 of the fau 12 todrive the latter.

Part of the air pressurized by the fan 12 is discharged through a bypassnozzle 22 to provide a propulsive force. The remainder of thispressurized air enters the compressor 14 for the generation of a hot gasstream, as above described. The hot gas stream, after passing throughthe fan turbine 20, is then discharged through an exit nozzle 24 toprovide an additional propulsive force.

The fan 12 comprises a rotor 26 having a single, circumferential row ofairfoil-shaped blades 28 rotating |within a shroud 30. Air passes fromthe blades 28 to a row of stators 32, which properly direct thepressurized air towards the nozzle 22 and the core engine 10.

FIGURES 2-8 illustrate in detail one of the blades 28. The blade itselfhas an airfoil-shaped portion 34 which terminates at its inner end in aplatform 36. The platforms of adjacent blades are closely spaced inabutting relation to define the inner flow path of the air passingthrough the fan. A tang 38 is provided at the base of the blade 28 formounting it in the usual fashion on the rotor 26.

As is evident from the drawing, the blade 28 projects radially from theaxis of rotation of the rotor 26 and has an aerodynamic airfoil crosssection relative to its length. Design of such aerodynamic crosssections is a highly refined art, dependent upon several parameters suchas speed, length, desired pressure ratio, etc. For any given compressorthere will be :a theoretical optimum curvature of the sides of the bladeand, particularly for the leading edge portion wherein there is arelatively sharp curvature usually through somewhat less than l80 to theopposite sides of the blade. The opposite sides of the blade are spacedequidistant from `a chord extending between the leading and trailingedges of the blade. These relationships are illustrated in FIGURE 3.

The leading edge of the blade 28 is characterized by incremental,lengthwise portions 40 being inclined relative to the air ow path andconnected by portions 42 to form teeth having tips rwhich overlie curvedcrotches at the inner convergence of the surfaces 40 and 42.

Assuming that the teeth at their tips have the theoretically desiredleading edge curvature, it will be seen from FIGURES 6 and 7 that theinclined portions 40 substantially throughout their length approximatethis desired curvature. The surface 42 is preferably flat at the outerends of the teeth and is progressively crowned (FIGURE 8.) toward thecrotch so that the curved crotch may be in the form of a saddle blended'with the curvature of the inclined portion 40.

For maximum effectiveness in resisting erosion with little or no adverseeffect on aerodynamic characteristics, it is preferred that the inclinedportion 40 be disposed on an angle a, relative to the direction of airflow, preferably between and 75. It is further preferred that theinterconnecting portions 42 be inclined on an angle f3 between 0 and 20relative to the direction of air flow. Both of the portions and 42, itwill be noted, are inclined in the same direction relative to air flow,giving a swept sawtooth effect wherein the tips of the teeth protect thecrotches as previously pointed out. It is preferred that the teeth beangled toward the outer end of the blade, as illustrated, to minimizestress concentrations.

FIGURES 9 and 10 illustrate a modified form of the 4. invention whereinthe tips of the teeth formed by the portions 40 and 42 are pointed attheir outer ends. This illustrates that some small deviation from thetheoretical airfoil curvature may be tolerated and, in fact, desirablefor certain materials, as will be more apparent from the followingdiscussion.

The provision of the incremental, inclined leading portions 40 has beenfound highly effective in preventing or minimizing erosion resultingfrom rain particles or the like entrained in `air which passes by thecompressor blades. The inclined portions provide an angle of incidencefor the rain particles which minimizes the erosion effects. The anglemay vary through fairly wide limits, as indicated by the preferredlimits for the angle a given above. Further, the swept configuration ofthe resultant teeth insures that all portions of the leading edge willhave such :an inclined incidence surface. This is to say that the tipsof the teeth protect the crotches from direct impingement of airparticles thereon. Further, the cross section `of the teeth (related tothe lengthwise direction of the blade) approximates the optimum airfoilshape so that the aerodynamic characteristics of blades formed inaccordance with the present invention will show little or no loss inefficiency and conceivably may show an increase in efliciency.

As was mentioned above, the angled incidence of rain particles on theblade is necessary and the pointed tips of FIGURES 9 and l0 may berequired to provide increased angularity for certain materials,particularly the plastics mentioned above.

The use of incremental, inclined portions has been discussed inconnection with the first row of fan blades where erosion conditions areusually most severe. However, the same feature can be used to advantageon stators as well and also straight turbojets. It will further beapparent that deviations from the precise configuration disclosed willfall Within the present inventive teachings, the scope of which istherefore to be derived solely from the following claims. Having thusdescribed the invention, what is claimed as novel and desired to besecured by Letters Patent of the United States is:

1. In a gas turbine engine having an axial flow compressor whichincludes a rotor having radially projecting blades at the compressorinlet,

each of said blades having an aerodynamic, airfoil portion extendingradially of the axis of the rotation of said rotor and having leadingand trailing edges relative to the air flow therepast, said leading edgeportion having a theoretical optimum curvature blending with theopposite sides of the blade which are equidistant from a median chordline extending between the leading and trailing edges of the blade,

`characterized in that the leading edge, at least at its outer endportion, has relatively small, lengthwise incremental portions inclinedlat an angle a of 30 to relative to the air flow path approaching saidblade, v

said inclined portions have said optimum curvature substantiallythroughout their lengths, and

said inclined portions are interconnected by edge portions which areinclined at least 30 relative to the air flow path therepast,

whereby said inclined portions have a high resistance to erosion and theblade, as a whole, has a high aerodynamic efficiency.

2. In a gas turbine engine as in claim 1 wherein,

said interconnecting portions are inclined at an angle of O-30 relativeto said gas flow path,

said interconnecting portions being inclined relative to said gas flowpath in the same direction as the lengthwise incremental portions toform teeth having crotches protected by the tips thereof from rain orthe like entrained in said air stream, Iwhile at the same time providinga leading edge which is resistant 5 6 to the corrosive effects of rain,or the like, with little 4. In a gas turbine engine as in claim 2wherein, or no adverse effect on the aerodynamic characteristic theextreme tips of said teeth are pointed. of the blade. 3. In a Igasturbine engine as in claim 2 wherein, References Cited theinterconnecting portions are substantially flat at the 5 UNITED STATESPATENTS tips of the teeth and are progressively crowned toward 1,862,8276/1932 Parsons et aL 170 159 the crotches, the curvature of said crownbeing blend- 3,365,126 1/1963 Stoffer et aL 170 159 ed With thecurvature of said inclined portions at said Crotches. EVERETTE A.POWELL, IR., Primary Examiner.

